var stbScore = parseFloat(prompt("请输入STB课成绩：",''));
var javaScore = parseFloat(prompt("请输入JAVA课成绩：",''));
var sqlScore = parseFloat(prompt("请输入SQL课成绩：",''));
console.log("STB课成绩：" + stbScore);
console.log("JAVA课成绩：" + javaScore);
console.log("SQL课成绩：" + sqlScore);
console.log("----------------------");
console.log(' STB\tJava\tSQL ');
console.log(` ${stbScore} \t ${javaScore} \t ${sqlScore} `);
console.log("----------------------");
var cha = Math.abs(javaScore - sqlScore);
console.log('Java和SQL的成绩差是：' + cha);
var avg = (stbScore + javaScore + sqlScore)/3;
console.log('三门课的平均分是：' + avg.toFixed(2));